Does Cohabitation Extend Life? Yes, But Married Individuals Live Longer

Cohabiting partners live longer than singles, according to recent research by Jesper Lindmarker, Martin Kolk, and Sven Drefahl published in the European Journal of Population. Even those of us who believe marriage is more than a piece of paper and essentially better than cohabitation can easily accept this finding. After all, we don’t claim that white bread is devoid of nutrients, even while we hold that wheat bread is more nutritious. 

The new study based on Swedish register data highlights that partnerships are, on average,  health-producing resources without denying that partners can also damage each other’s health.

Relationship Status and Life Expectancy

I appreciate the way another study, the Couples HEalth Research and Intervention Studies (CHERISH) project at the University of Southampton, succinctly emphasizes how couples’ shared health behaviors can be both bad and good:

Couples often share the same social and physical environments, adopting similar health behaviors that can adversely impact upon their quality of life. But living a shared life can be the foundation upon which to build a mutually supportive environment that can help couples make the positive changes that lead to better health.

CHERISH collected data from older adults in Kwa-Zulu Natal, a South African province where the HIV prevalence rate exceeds 15% and more than one-third of dwellings lack piped water. Even in this adverse physical environment, couples supported each other’s health. Management of health threats like diabetes and hypertension can be facilitated when the couple thinks of dietary change as their agenda rather than the diagnosed partner’s problem. Being part of a “we” rather than just an “I” can increase both motivation and follow-through. Shared resources matter too: two people may not live as cheaply as one, but they certainly can live more cheaply than one plus one. 

In this new study, the researchers note: 

partnerships confer substantial protective benefits. Social support plays a crucial role: a partner not only provides companionship, but also monitors health, encourages adherence to medications, and offers emotional comfort that counteracts the negative effects of stress.

These benefits of being part of a couple can be expected to matter more as health challenges pile on, an unfortunately ubiquitous consequence of aging. Not surprisingly, then, union status matters more for mortality later in life. Young adults rarely die—differences between singles, cohabitants, and marrieds are consequently smaller. But folks in their 50s and 60s are more likely to be coping with diabetes and other illnesses that require lifestyle changes, and Lindmarker and his coauthors found a stronger association between union status and mortality at older ages. They also found that cohabitants fare better than singles but not as well as marrieds, a pattern that is consistent with other research (reviewed here). We’re back to white bread delivering some of the same nutrients that wheat bread does.

Why Married Individuals Live Longer

My analogy, however, rests on the assumption that there is something essentially different between a marriage and a cohabiting union. The evidence points that way. For instance, worrying about relationship dissolution has health consequences, and cohabitors are more likely to worry about the future of their partnership than marrieds. It makes sense that a partnership requiring less commitment would inherently foster more uncertainty about the future. 

Consistent with prior research, when it comes to mortality, cohabitants fare better than singles but not as well as marrieds.

Cohabitants, however, differ from marrieds in other ways. For instance, they are more likely to have been in a previous union, and divorce and widowhood are also associated with health consequences. This isn’t a causal story: that is, people whose prior relationships may have compromised their health are more likely to be cohabitants (a very different claim than that cohabitation itself delivers fewer health benefits than marriage). Most studies that statistically controlled for “pre-existing conditions” like these—social scientists like to call them “selection factors”—still find that the health of cohabitors falls between that of singles and marrieds.

An Essential Difference

Lindmarker and colleagues’ work was statistically rigorous. Swedish register data gave them full partnership histories (all previous entries and exits from coresidential unions) along with a number of other background factors that could have “selected” Swedes into singleness, cohabitation, or marriage. That means that when they found that even though cohabitors have better health than singles, married individuals still have better health than cohabitors, they were likely identifying differences in the experience of the unions themselves. That is, they were likely picking up on an essential difference. 

It is impossible to prove an essential difference because a statistical model cannot have a variable controlling for every single background factor that might matter. For instance, a particular childhood experience might dispose an adult to eschew marriage (or embrace it) and also matter for his or her health. But while it is impossible to prove that marriage causes superior health benefits relative to cohabitation, the researchers went a step further by including a variable identifying sibling groups in the background factors they controlled for. By doing so, they were able to control for shared histories at a very personal level. This means that the difference in the health benefits between cohabitation and marriage that they measured were net of a bunch of other factors that the researchers could not observe (that were statistically controlled to the extent that they were shared by siblings, whatever they were). In other words, the statistical power driving their results came from differences between siblings in longevity as a function of what kind of unions the siblings were in. All their shared family history and even their shared genetics could no longer drive the differences. While this doesn’t prove that marriage causes people to live longer than cohabitation, this new research is strong evidence that it does. 

The author’s emphasize the health benefits likely caused by cohabitation, which matter more for population health now than they did decades ago, because today’s elderly have more experience with cohabitation. So while we may have doubts about the spiritual, economic, and social costs of a union recipe that does not include marriage, we can still acknowledge the accumulating evidence that being in a partnership, rather than living alone, promotes health and happiness.

Laurie DeRose is a senior fellow at the Institute for Family Studies, Assistant Professor of Sociology at the Catholic University of America, and Director of Research for the World Family Map Project.